Sunday, February 26, 2006

Sacramento Flooding

From: "Wendell Huffman" wwhuffma@clan.lib.nv.us

In rlhsgroup, "cnefan" wrote:

For the past couple of months or so, the Sacramento Bee newspaper has been harping on the fact that the City of Sacramento and quite a bit of the surrounding area appears to be quite vulnerable to possible flooding from both the American River and the Sacramento River. ... What I would like to know is what, if any, contingency plan is in place by the California State Railroad Museum to get their's and the R&LHS's vast collection of historical material out of the basement of its library building before the next possible deluge hits the area?

That is a good question, but one I will avoid simply because I don't know. I do know, however, a bit of the history of the Sacramento area levees and Sacramento's geography (thanks to the connection between those and the railroad).

Front street and I street, and the entire railroad yard to the north are essentially the level of the top of the levee in that area. I cannot imagine the levees at those points are at all vulnerable as they are essentially blocks wide. South of I street and east of Front the streets themselves are at levee level, though the actual grade of the blocks surounded by those streets are over eight feet below street/levee grade – which is close to the original grade of the city in that area. Those blocks are indeed sinks, without natural drainage, and which might indeed fill up with water should a flood overtop a levee. But again, because of the width of the Front Street levee and the massive levee-grade earthwork of the railroad yard to the north, a break at those points is unlikely.

South of R on Front the Sacramento levee becomes just a levee, though surmounted with a railroad track. Many of the streets south of R street actually drop down to the general level of the city's original grade at that point. This is very apparent if you drive south on Front Street. South of R street there is a noticable drop.

East of about 12th street the earthwork of the railroad yard narrows and the north levee becomes just that – a levee; though surmounted with a railroad track. If there is any vulnerablity in the levees protecting the old part of Sacramento (say from Front to 65th, or south to Broadway, it would be in the old north and east levee (which support the SP tracks from the railyard to Elvas and Brighton, and south of R street). Frankly, it seems to me that while any break in levees in those areas might flood a good portion of Sacramento (generally along the McKinley Park-Sutter's Fort-South Side Park channel of the old Burn's Slough), I really doubt flood levels would ever rise enough to flood back into the northwest corner of the old city in the "Old Sacramento" district. Though there might be local flooding due to rainwater accumulation in those blocks surounded by the streets raised to levee level. However, because the railroad is on that levee, and was widened and maintained by them, it is a significant earthwork and is probably the strongest levee in the area.

My reason for doubting a flood would ever back up into the old part of town is simply that the waters would drain off to the south and back into the Sacramento River below the city. This was always the traditional flooding pattern: a levee break in the area near what is now Elvas, flooding south through the city along the Burn's Slough. The general disaster of the 1861-62 flood was caused by the fact that the city fathers had allowed the Sacramento Valley Railroad to fill in their trestle crossing of Burns Slough (between 17th and 21st Street). When the levee broke, the waters raced down Burn's Slough until the hit the railroad's new embankment, and backed up into the city. The R street levee – as it came to be called – was opened up in four places – where city streets actually passed under the railroad, and after 1900 the R street levee was actually removed and the railroad lowered to street level.

East of Sacramento – east of the so called east levee – there is some vulnerability to flooding. There never was much of a levee along the south side of the American River. Suburban development there (River Park, the college, and College Park) began with the erection of Folsom dam (the "high dam" – there was an earlier dam dating to the 1880s) . And, just as with the floods of 1861-62, the railroad east of Sacramento has the potential to make things bad.

To give some indication of grade, the railroad's official elevation at Sacramento station is 35 feet. Going east along the old SVRR (Folsom-Placerville branch) the grade ascends to 54 feet at Brighton Jucntion (more-or-less 65th and Folsom Blvd), but then goes down again. At Ramona (Power Inn Road) is is down to 49 feet; by Perkins it up to 52 feet, then another half mile back down to 48 feet, and isn't back up to 60 feet until Mayhew Road. This railroad grade would hold water in the College Park area and cause significant flood damage, perhaps clear around into River Park and the college, but it would spill over the railroad in the Power Inn Road area well before it flooded west into Sacramento. This is what it did in 1907 – when the railroad between Perkins and Manlove was washed out. Ironically, such a flood would fill in those massive gravel pits between the railroad and 14th Avenue and between Watt and 65th – the pits from which much of the material came which was used to fill in the streets in the old part of town, raising them to the grade of the levee.

While Folsom dam has the potential to prevent a flood along the American River, things can go wrong. I recall when Hell Hole dam on the Rubicon broke many years ago. Folsom began discharging at emergency levels to make room in its reservor for the expected influx. As a result, the American River below Folsom was lapping the top of the levee and acrually spilled over in some areas.

There was a plan generated many years ago to dig a channel from the American River south west to the Sacramento River below Freeport – genrally along the south side of the old Freeport Railroad grade. This would have served the same protection from the flooding American as the Yolo Bypass serves to protect Sacramento city from a flooding Sacramento River. Folsom Dam eliminated the need for this.

Probably the greatest potential problem is north of Sacramento, between the Sacramento, American, and Bear rivers. The city-county was happy to have the developers move in, but the only protection is Folsom dam. The levees which protected those areas are no doubt untrustworthy – and now the people who bought into those developments are expecting the rest of us to protect them. But flooding there would not effect the old part of the city.

While the basement at CSRM might fill up with accumulated rain water should the power be out and the pumps inoperable, it is very unlikely that river flood waters would ever back up across the railroad yard or I street to fill in that basement. I hope CSRM has their own adequate sump pump and the generator to run it.

(Many years ago my father was a senior engineer with the California Department of Water Resources. As such, he was assigned a mile of levee to monitor and supervise during flood emergencies. Every time it rained hard and the rivers backed up, he always wondered how his levee was doing. Seems that in the process of bureaucracy, they just never got around to telling him just where his mile of levee was located!)

4 Comments:

Anonymous said...

"Scientific American magazine published an article quoting Leland Stanford of the Central Pacific Railroad, who observed that when they were blasting with dynamite, rain not only fell in the driest areas but ceased when blasting stopped."

Of course, the CPRR never used dynamite, so maybe the quotation is as accurate as the kaboom theory of rainmaking.